HF Flyback driver

[darkspeed]

NOTE: Im not responsable for what you do to yourself with this device.. I have no control over the laws of natural selection.. use at your own risk.. it will hurt you..




>>> The final version of this project can be found on page two - http://www.overunityresearch.com/index.php?topic=206.msg2304#msg2304




This is a flyback driver I threw together today for replacing the nst in the Don Smith test rig.

It runs off a small 12vdc battery. << currently running it off of a 24vdc 5amp regulated supply for more power

It works as an amplifier using the +10v signal from a signal generator to drive the gate on a Mosfet.

The mosfet drives a 4 turn coil on the flyback and a current limiting resistor.

There is a 95v neon on the negative of the L2 to locate resonant frequencies.

The natural RF is 6khz - 12khz - 24khz ...

To use other frequencies like 70khz for example you must fine tune the pulse width in the 10us range to reestablish the resonant frequency. The tuning on this is very narrow!

At the moment I have it tuned down to 2kv at 70khz and it is super stable      

At the moment it is only running at 15w from a 12v battery. <<< I have increased it

[Grumpy]

Hey DS, can you provide more info on this little unit, like parts list and schematic?  I'd like to have one of those.

[darkspeed]

Sure G. I will try to get one together tonight.

This is set up specifically for stable pulsed dc ( most on youtube are set up to generate huge arcs )

Its super simple

VERSION 1____________________(STABLE)___________________________________________________________________________

1 - 12v battery
1 - IRF840 - 8 amp 500v mosfet ( can also use like a IRFP250 for more power 33amp )
1 - heatsink
3 - IN5408 - 1000v 3 amp diodes ( or 1 - 1000v 10a diode )
1 - 10,000v 1a diode  ( could use 0.1a diode )
4 - 8 ohm 20w non inductive resistor ( radioshack )
1 - pair of red / black binding posts  ( radioshack )
1 - rca jack for signal in ( could be surface mount BNC )  ( radioshack )
1 - NT2 neon bulb
1 - Flyback transformer ( i dont have a part number on this one - most any open frame flyback will work )
1 - PCB ( radioshack )
2 - ceramic insulators
4 - PBC legs ( i used insulators )
1 - meter of 20awg magnet wire





VERSION 2 _______________________(MORE POWER)____________________________________________________________________

1 - 12v battery
1- 24vdc 5 amp regulated supply
1 - IRF840 - 8 amp 500v mosfet ( can also use like a IRFP250 for more power 33amp )
1 - IRF3205 110amp 55v mosfet ( found one in my parts bin and it works much better! )
1 - FDH44N50_Q - Single N-Ch 500V 44amp < needed a higher voltage mosfet to survive the transients - works great
1 - heatsink
3 - IN5408 - 1000v 3 amp diodes ( or 1 - 1000v 10a diode ) <<< too slow rtt eventually start to smoke at increased power
1 - 625-FES16JT-E3 16 Amp 600 Volt ultrafast diode + heatsink ( diode across coil to null bemf )
1 - 10,000v 1a diode  ( could use 0.1a diode )
4 - 8 ohm 20w non inductive resistor ( radioshack ) ( could also use an inductor in place of the power resistor ) << I removed the resistors and am using a 5amp regulated supply
1 - pair of red / black binding posts  ( radioshack )
1 - rca jack for signal in ( could be surface mount BNC )  ( radioshack )
1 - NT2 neon bulb
1 - Flyback transformer ( i dont have a part number on this one - most any open frame flyback will work )
1 - PCB ( radioshack )
2 - ceramic insulators
4 - PBC legs ( i used insulators )
1 - meter of 20awg magnet wire



Flyback - The flyback I used is overkill but I wanted to have it run cool and be able to add more mosfets to increase power if needed. Some flybacks have an internal diode, you need to know this!
Diode - The diodee between the signal generator and the gate is optional. The mosfet needs 10v on the gate to fully open so depending on what your sig gen puts out you may want to delete this diode as there will be a voltage drop across it.

Other options would be:
- add a 555 driver with variable pulse width << very important!
- add a full bridge on the output
- run multiple flybacks from a shift register to get much higher frequencies
- bigger mosfets with lower ohm higher watt resistor  << did this works better
- increase drive voltage to 24vdc  << did this works better






Photos of VERSION 1

[Grumpy]

Won't you need a cap across the output if you are pulsing some sort of arbitrary load?  If so, what size?

EDIT:

With hv switches, couldn't you use one power supply?  I guess then you need the cap that I asked about, but probably not with multiple supplies.



This has been holding me up and I never thought of using multiple power supplies and switching LV

[darkspeed]

Well my use would be to drive a tuned primary (inductor / capacitor)  through a calibrated spark gap like one of the 1B22 tubes. So the only time the flyback would see a load is when the spark gap makes.

Is this what you mean? or did i not understand your question..





Flash lamp and small arc at 70khz
Checking amp draw

[darkspeed]

Ah. ok the supply is a battery and the signal is from the sig gen so they are seperate

The battery is switched through the mosfet and only pulses the drive coil. It is very short leads to a 7ah motorcycle battery.

The sig gen puts a +10v pulse into the gate of the mosfet to switch the pulse coil.

I try never to use the same supply!




Output from the HP Signal generator is fed into the Wavetek for pulse width modulation.
The output of the WaveteK drives the monitoring scope and the gate on the IRF840

[darkspeed]

Here you go

I just changed this photo - i forgot a diode in the drawing..

I added a diode across the drive coil



VERSION 1 Diagram

[Peterae]

Hi Ds
Looks nice and easy to build, just what the Don smith guys needed, you mention it goes to 70khz ok which is great

Peter

[darkspeed]

Thanks Peter..

There is also the option of skipping the signal generator and just using a pickup coil somewhere in the Don Smith system to retrigger this at a resonant frequency but it would require a circuit to adjust the pulse width from the pickup coil.




Here are the settings I am using.
The most important setting is the Vernier fine tune knob on the WIDTH dial.
It is used to retune to a resonant point. The tuned point is NARROW!

[Grumpy]

Ah. ok the supply is a battery and the signal is from the sig gen so they are seperate

The battery is switched through the mosfet and only pulses the drive coil. It is very short leads to a 7ah motorcycle battery.

The sig gen puts a +10v pulse into the gate of the mosfet to switch the pulse coil.

I try never to use the same supply!

can you use this to drive several coils sequentially?

[darkspeed]

Yes.

Sig gen > shift register > mosfets on the outputs of shift register > mosfets drive coils  

you can make a HV array with a diode on the output of each coil all tied together on the output

70khz... X4 ... x6... what ever you want


or you could do a 4017 decade counter < but i prefer shift registers

sig gen > decade counter > mosfets on the outputs of shift register > mosfets drive coils  

In this case:
- the pulse coils run off a battery
- decade or register and mosfets run off a 15vdc supply
- sig gen only provides the timing to the decade or register..




Here is a good example : http://www.doctronics.co.uk/4017.htm

Replace the LEDs with mosfets and replace the 4093 with the input from the signal generator.





Standing wave in a tube of Xenon gas                     

[Grumpy]

Thanks.  I have all of that.

How do I keep the voltage from dropping when the switch is on? I have a ap across the hv output, but it may be too small.

[darkspeed]

Describe that a little better.. Which voltage?

[Grumpy]

flyback output

[darkspeed]

Thanks.  I have all of that.

How do I keep the voltage from dropping when the switch is on? I have a ap across the hv output, but it may be too small.

Gap or cap? are you saying a cap across the output drops the voltage?

look at the photo i posted with the strobe bulb. what are you driving the primary with? how many amps / volts?

Did you usee the neon bulb on the single terminal of the flyback output to find a resonant frequency? you may be out of tune.

Using a set pulse width you are limited to natural resonant frequencies of the L2 ( hv output coil )
Using variable pulse width you can re-tune to any frequency you want but the tuning sweet spot is freakishly narrow.
That is what the neon is for - it will glow when it is in tune with no load on the output - loaded it will go out.

[Grumpy]

How do I size C1 and C3 - see attached:

Assumed that their are ten swtiching circuits driving different coils sequentially from the same supply.

Switches are triggered sequentially from a shift register clocked by a sig gen.

Say the PS is 2kv and I want it to stay within 2%.

[darkspeed]

G - I have not had my coffee yet so im still confused

The flyback drives a full bridge and each pulse is stored in C1 or C3?

When is T1 switched? or is it an antenna?

L is your coil to be pulsed?

L and C3 form a half resonant circuit when T1 closes

Im horrible at electronics 

[Grumpy]

flyback thru bridge charges c1/c3

L is coil being pulsed (only one is shown), but there are 10 being pulsed sequentially - all running from C3 connections - so 10 mosfets and coils.

[darkspeed]

So C1 and C3 would charge with the joules from one pulse long enough for the T1 to switch 99% of that stored energy across one of the 10 coils (L) in sequence?

This is apposed to using multiple flybacks? Interesting.. Im not sure how to correctly predict the pulse output without testing it.

What are you using for T1 ??

[Grumpy]

T1 is a dc switching pwr supply - 1ma at 2kv

[darkspeed]

_____________________VERSION 2________________________________________

Big heat sink is for the mosfets

Small heat sink is for the diodes across the drive coil

Full bridge output on flyback output

Built on cutting polypropylene boards

The fan is required!

[Grumpy]

poly boards are great!

are you going to drive the tetrahedral unit with this?

[darkspeed]

Not yet 

This was to see if I could get more power at higher frequency for the don smith testing.

This is the first of the three amps I am going to try on it  - to see what works best..


Did you figure out your capacitors?

[darkspeed]

FINAL VERSION!!! A lot more powerful---

The output is a brush discharge like a HF tesla coil

It seriously screws with the radio - even with the volume knob turned all the way down  :

Striped the core down bare
Made a secondary out of 4000' of 28awg
Made a multi tap primary out of 20awg
Added a 12v regulator to drive the cooling fan + small heatsink
Still driving it with a 24v 5a supply

The 28awg secondary will take a lot of power before it fails.

I ran it up to 500khz and it was still drawing an arc       The output through the full bridge would result in 1mhz < need to check that

[darkspeed]